JP7764339B2 - Secondary batteries, battery packs, vehicles, and stationary power sources - Google Patents

Description

Embodiments of the present invention relate to secondary batteries, battery packs, vehicles, and stationary power sources.

Unlike lithium ion secondary batteries with non-aqueous electrolytes, lithium ion secondary batteries with aqueous electrolytes generate gases, mainly _H2 , during charging and discharging. Also, unlike lead-acid batteries, lithium ion secondary batteries with aqueous electrolytes do not generate _O2 , making it difficult to deal with the generated gases using gas treatment methods based on the recombination of _H2 and _O2 .

Regarding the treatment of gas generated inside batteries, there have been reports of chemical recombination using catalysts or hydrogen storage alloys in nickel-metal hydride (Ni-MH) and lead-acid batteries. Furthermore, there have been reports of hydrogen storage in alloys in lithium-ion secondary batteries with non-aqueous electrolytes.

However, these methods are limited to nickel-metal hydride batteries and lead-acid batteries in which _H2 and _O2 coexist inside the battery, or lithium-ion secondary batteries with non-aqueous electrolytes in which the amount of _H2 dissolved in the electrolyte is relatively high, and have the problem that they cannot be applied to lithium-ion secondary batteries with aqueous electrolytes that do not satisfy these conditions.

JP 2014-164800 A JP 2017-84504 A Japanese Patent Application Laid-Open No. 2021-180084 International Publication No. WO2008/056536

The problem to be solved is to provide a secondary battery that can suppress an increase in internal pressure due to gas generation, a battery pack equipped with this secondary battery, a vehicle, and a stationary power source.

According to an embodiment, a secondary battery is provided that includes a positive electrode, a negative electrode, an aqueous electrolyte, and a gas processing structure. The gas processing structure can process hydrogen gas by being electrically connected to the positive electrode.

According to an embodiment, a battery pack including a battery according to the embodiment is provided.

Furthermore, according to an embodiment, a vehicle equipped with the battery pack of the embodiment is provided.

Furthermore, according to an embodiment, a stationary power source equipped with a battery pack of the embodiment is provided.

FIG. 1 is a plan view illustrating an example of a secondary battery according to an embodiment. 2 is a cross-sectional view of a laminate included in the secondary battery shown in FIG. 1 cut along the thickness direction. 2 is a cross-sectional view of the electrode group of the secondary battery shown in FIG. 1 cut along the thickness direction. FIG. 10 is a plan view showing another example of the secondary battery according to the embodiment. FIG. 2 is a diagram showing an electric circuit of a part of the configuration of the secondary battery according to the embodiment. FIG. 10 is a perspective view showing another example of the gas treatment structure of the secondary battery according to the embodiment. FIG. 10 is a perspective view showing still another example of the gas treatment structure of the secondary battery according to the embodiment. FIG. 10 is a perspective view showing still another example of the secondary battery according to the embodiment. FIG. 1 is an exploded perspective view schematically illustrating an example of a battery pack according to an embodiment. FIG. 9 is a block diagram showing an example of an electrical circuit of the battery pack shown in FIG. 8 . 1 is a partially see-through view schematically illustrating an example of a vehicle according to an embodiment. FIG. 1 is a block diagram showing an example of a system including a stationary power supply according to an embodiment.

The following embodiments are described with reference to the drawings. In the following description, components having substantially the same functions and configurations are designated by the same reference numerals, and repeated explanations may be omitted. The drawings are schematic, and the relationship between thickness and planar dimensions, the thickness ratio of each layer, and the like may differ from the actual ones. Furthermore, the drawings may include portions in which the dimensional relationships and ratios differ from each other. Furthermore, all descriptions of one embodiment also apply to descriptions of other embodiments unless explicitly or obviously excluded. Each embodiment exemplifies an apparatus or method for embodying the technical idea of the embodiment, and the technical idea of the embodiment does not specify the materials, shapes, structures, arrangements, etc. of the components described below.
(First embodiment)
A secondary battery according to a first embodiment will be described with reference to FIGS. 1 to 8. FIG. 1 is a plan view showing an example of a secondary battery, with the exterior member partially cut away to facilitate understanding of the internal structure of the exterior member. As shown in FIG. 1, the secondary battery 1 includes an exterior member 2 and a stack 3 housed within the exterior member 2. The stack 3 includes an electrode group 4 and a gas treatment structure 5. The secondary battery 1 further includes a positive electrode terminal 6 electrically connected to the positive electrode of the electrode group 4, a negative electrode terminal 7 electrically connected to the negative electrode of the electrode group 4, wiring 8 for electrically connecting the positive electrode terminal 6 to the gas treatment structure 5, and a resistor 9 interposed in the wiring 8. In FIG. 1, the main surface of the electrode group 4 is parallel to the xy plane, and the thickness direction of the electrode group 4 is parallel to the z-axis direction. The main surface of the electrode group 4 is rectangular. The long side direction of the electrode group 4 is parallel to the y-axis direction, and the short side direction of the electrode group 4 is parallel to the x-axis direction.

As shown in Figure 3, the electrode group 4 is a stacked electrode group. The stacked electrode group 4 has a structure in which positive electrodes 10 and negative electrodes 11 are alternately stacked with separators 12 interposed therebetween. The electrode group 4 includes a plurality of positive electrodes 10. Each of the plurality of positive electrodes 10 includes a positive electrode current collector 10a and a positive electrode mixture layer 10b supported on both sides of the positive electrode current collector 10a. The electrode group 4 also includes a plurality of negative electrodes 11. Each of the plurality of negative electrodes 11 includes a negative electrode current collector 11a and a negative electrode mixture layer 11b supported on both sides of the negative electrode current collector 11a.

The positive electrode current collector 10a of each positive electrode 10 includes a portion on one side where the positive electrode mixture layer 10b is not supported on any surface. This portion functions as a positive electrode current collector tab. The portion functioning as the positive electrode current collector tab does not overlap with the negative electrode 11. In addition, the multiple positive electrode current collector tabs are electrically connected to a strip-shaped positive electrode terminal 6. The tip of the strip-shaped positive electrode terminal 6 is extended outside the exterior member 2.

As shown in FIG. 3, the negative electrode current collector 11a of each negative electrode 11 includes a portion 11c on one side where the negative electrode mixture layer 11b is not supported on any surface. This portion 11c serves as a negative electrode current collecting tab. The negative electrode current collecting tab does not overlap with the positive electrode 10. The negative electrode current collecting tab is located on the opposite side of the electrode group 4 from the positive electrode current collecting tab. The negative electrode current collecting tab is electrically connected to a strip-shaped negative electrode terminal 7. The tip of the strip-shaped negative electrode terminal 7 is located on the opposite side of the positive electrode terminal 6 and is pulled out to the outside of the exterior member 2.

An aqueous electrolyte (not shown) is held in the electrode group 4.

Figure 2 is a cross-sectional view of the laminate 3 cut in the stacking direction (z-axis direction in Figure 1). For ease of explanation, the separator 12 is omitted from the electrode group 4 shown in Figure 2. The gas processing structure 5 is disposed on one main surface of the electrode group 4. Here, the main surface of the electrode group 4 is a plane parallel to the xy plane in Figure 2. The gas processing structure 5 may be in contact with the main surface of the electrode group 4, or may be disposed with a gap between it and the main surface of the electrode group 4. The gas processing structure 5 includes a conductive porous substrate 13 and a gas processing layer 14 supported or laminated on one main surface (a plane parallel to the xy plane) of the porous substrate 13. The gas processing layer 14 contains, for example, a precious metal catalyst. The main surface of the porous substrate 13 of the gas processing structure 5 faces the electrode group 4. The porous substrate 13 is located between the gas processing layer 14 of the gas processing structure 5 and the electrode group 4. The porous substrate 13 may be in contact with the electrode group 4, or there may be a gap between the electrode group 4 and the porous substrate 13. One end of the wiring 8 is electrically connected to the porous substrate 13. The wiring 8 is electrically connected to the positive electrode terminal 6 via a resistor 9. Note that in FIG. 2, the main surface of the porous substrate 13 of the gas processing structure 5 faces the electrode group 4, but the main surface of the gas processing layer 14 may be in contact with the electrode group 4, or may face the electrode group 4 with a gap therebetween.

The exterior member 2 is formed, for example, from a laminate film including a metal layer. The exterior member 2 is sealed in a state in which the tips of the positive electrode terminal 6 and the negative electrode terminal 7 protrude along the y-axis direction in Figure 1.

In the secondary battery containing the aqueous electrolyte described above, electrolysis of water occurs, generating hydrogen gas, for example, during float charging or charge/discharge cycles. The hydrogen gas permeates the porous substrate 13 of the gas processing structure 5 within the exterior member 2 and reaches the gas processing layer 14. The gas processing structure 5 is electrically connected to the positive electrode terminal 6 of the positive electrode 10 via a resistor 9. Therefore, in the gas processing layer 14, the hydrogen gas is converted into water according to the following reaction formula (A). This reaction can occur when _E0 is at a potential of −0.83 V.

The above reaction consumes hydrogen gas. The generated water can function as a solvent for the aqueous electrolyte. Meanwhile, the positive electrode 10 may self-discharge, for example, according to reaction formula (B). Reaction formula (B) shows the discharge reaction of the positive electrode when LiMn ₂ O ₄ is used as the positive electrode active material. This discharge reaction may occur at a potential of +0.95 _V.

The overall reaction equation combining equations (A) and (B) is shown below in (C).

The electromotive force E of reaction (C) is 1.78 V.

As explained above, by electrically connecting the gas processing structure 5 to the positive electrode 10, a spontaneous recombination reaction between gaseous H ₂ and hydroxide ions (OH ⁻ ) can occur at an electromotive force of approximately 1.78 V, accompanied by self-discharge of the positive electrode. As a result, hydrogen gas accumulation within the secondary battery can be suppressed, thereby suppressing an increase in the internal pressure of the secondary battery and improving charge/discharge efficiency. When gas accumulates within the battery, the liquid junction on the electrode surface is obstructed, reducing the electrode surface area that can contribute to charge/discharge, thereby reducing the discharge capacity. This in turn reduces charge/discharge efficiency. Furthermore, since self-discharge of the positive electrode also occurs during the hydrogen gas treatment process, overcharging of the positive electrode can also be suppressed. Furthermore, because the gas processing structure 5 is electrically connected to the positive electrode 10 via the resistor 9, the current flowing through the gas processing structure 5 can be controlled to a constant level. This prevents excessive self-discharge of the positive electrode, thereby preventing overdischarge of the positive electrode.

In Figures 1 to 3, the gas processing structure 5 is arranged on the electrode group 4, but the arrangement of the gas processing structure 5 is not limited to this. For example, as shown in Figure 4, the gas processing structures 5 may be arranged side by side in the direction of the short sides of the electrode group 4 (the x-axis direction in Figure 1). In this case, a gap may be provided between the electrode group 4 and the gas processing structure 5. Furthermore, the embodiment is not limited to this arrangement, and the gas processing structures 5 may be arranged side by side in the direction of the long sides of the electrode group 4 (the y-axis direction in Figure 1).

1 to 4, the gas processing structure 5 is electrically connected to the positive electrode 10 via a resistor 9, but this is not limited to this. A switching element can be used instead of a resistor. This example will be described with reference to FIG. 5. FIG. 5 is a circuit diagram showing an electrical circuit including the gas processing structure 5 and the positive electrode 10. A switching element 21, such as a transistor, is electrically connected to the gas processing structure 5 via wiring 8a. The switching element 21 is also electrically connected to the positive electrode 10 via wiring 8b, and is configured to receive a signal via wiring 8c indicating that a predetermined voltage has been applied between the gas processing structure 5 and the positive electrode 10. With this configuration, as the charging of the positive electrode 10 progresses and the positive electrode potential increases (the positive electrode potential shifts to the noble side), the potential difference between the positive electrode 10 and the gas processing structure 5 increases. When a predetermined voltage is applied between the gas processing structure 5 and the positive electrode 10, this is transmitted as an electrical signal to the switching element 21 via wiring 8c. As a result, the switching element 21 turns on the conduction between the gas processing structure 5 and the positive electrode 10, causing a current to flow between the gas processing structure 5 and the positive electrode 10. This allows the gas processing structure 5 to process hydrogen gas according to formula (A). When the voltage application between the gas processing structure 5 and the positive electrode 10 is released, this is transmitted as an electrical signal to the switching element 21 via the wiring 8c. As a result, the switching element 21 turns off the conduction between the gas processing structure 5 and the positive electrode 10, thereby electrically insulating the gas processing structure 5 from the positive electrode 10. This allows the gas processing structure 5 to stop processing hydrogen gas. Therefore, when charging of the positive electrode 10 progresses and the internal pressure of the secondary battery increases, the necessary current flows through the gas processing structure 5, allowing gas processing to be performed.

In the secondary battery of this embodiment, the gas processing structure 5 may be electrically connected directly to the positive electrode 10 without a resistor or switching element. As an example, the porous substrate 13 of the gas processing structure 5 may be in direct physical contact with the positive electrode 10, or the porous substrate 13 of the gas processing structure 5 may be electrically connected to the positive electrode 10 via wiring or the like.

1 to 4 , the gas processing structure 5 is configured from a conductive porous substrate 13 and a gas processing layer 14, but the gas processing structure 5 is not limited to this. To increase the processing capacity of the gas processing structure, the gas processing structure 5 may include a plurality of conductive porous substrates 13 and gas processing layers 14. An example of this is shown in FIG. 6 . As shown in FIG. 6 , the gas processing structure 5 is electrically connected by a conductive member 22 to a resistor 9 that is electrically connected to a positive electrode terminal 6. The gas processing structure 5 includes a plurality of conductive porous substrates 13, a plurality of gas processing layers 14, and a plurality of electrolyte layers 23. A gas processing layer 14 is disposed on each of the porous substrates 13. An electrolyte layer 23 is disposed on each of the gas processing layers 14. The electrolyte layers 23 contain an aqueous electrolyte. The gas processing structures 5 are arranged so that the surfaces on which the electrolyte layers 23 are formed face in the same direction. The conductive member 22 includes a first conductive plate 22a, e.g., a Ti plate, and multiple second conductive plates 22b protruding from one side of the first conductive plate 22a. A resistor 9 is electrically connected to the other side of the first conductive plate 22a. The multiple second conductive plates 22b are made of, e.g., Ti foil and are spaced apart from one another on one side of the first conductive plate 22a. Each of the second conductive plates 22b contacts the porous substrate 13 of the gas-processing structure 5. The gas-processing structure 5 described above can increase the contact area with hydrogen gas, thereby improving processing capacity. Furthermore, the electrolyte layer 23 can retain water molecules generated by reaction formula (A), thereby maintaining a low water content in the porous substrate 13. As a result, hydrogen gas can be smoothly supplied from the porous substrate 13 to the gas-processing layer 14. Furthermore, the electrolyte layer 23 can supply OH ⁻ of reaction formula (A) to the gas-processing layer 14. As a result, the hydrogen gas processing capacity of the gas processing structure 5 can be improved.

The electrolyte layer 23 is not particularly limited as long as it contains an aqueous electrolyte, but examples include a gel electrolyte layer containing an aqueous electrolyte and a porous membrane retaining an aqueous electrolyte. The aqueous electrolyte may have the same composition as the aqueous electrolyte contained in the secondary battery, or it may be different.

1 to 4, the gas processing structure 5 is configured from a conductive porous substrate 13 and a gas processing layer 14. However, the gas processing structure 5 is not limited to this. The gas processing structure 5 may further include a layer having gas flow channels. This example is described with reference to FIG. 7. The gas processing structure 5 further includes a layer 25 having gas flow channels 24 supported on the other main surface of the conductive porous substrate 13. The gas flow channels 24 are recesses formed in the surface of the layer 25. The number of gas flow channels 24 can be one or more. In FIG. 7, multiple gas flow channels 24 are provided on the surface of the layer 25 along one direction 26 (the x direction or the y direction) at predetermined intervals. The provision of a layer having gas flow channels allows for smoother supply of gas generated from the electrode group to the gas processing layer 14. An example of a layer having gas flow channels is a fluororesin sheet having recesses. An example of a fluororesin is polytetrafluoroethylene (PTFE).

1 to 4 illustrate an example in which the positive electrode terminal 6 and the negative electrode terminal 7 of the electrode group 4 extend in opposite directions, but this is not limiting. For example, as shown in FIG. 8, the positive electrode terminal 6 and the negative electrode terminal 7 may extend in the same direction. The positive electrode terminal 6 and the negative electrode terminal 7 extend in the same direction from one end face of the electrode group 4. The positive electrode terminal 6 and the negative electrode terminal 7 are spaced apart from each other. A gas processing structure 5 is disposed in the space between the positive electrode terminal 6 and the negative electrode terminal 7. The gas processing structure 5 is electrically connected to the positive electrode terminal 6 via a resistor 9. This secondary battery makes effective use of the dead space between the positive electrode terminal 6 and the negative electrode terminal 7. Furthermore, complete immersion of the gas processing structure 5 in the aqueous electrolyte can be prevented, allowing for smooth gas supply to the gas processing structure 5.

The gas processing structure, positive electrode, negative electrode, aqueous electrolyte, separator, exterior member, positive electrode terminal, and negative electrode terminal included in the secondary battery of the embodiment will be described below.
(Gas Processing Structure)
The gas processing structure includes a conductive porous substrate and a gas processing layer. The gas processing layer is disposed on at least one surface (e.g., the main surface) of the conductive porous substrate. In the reaction of processing hydrogen gas by oxidation, water is produced, as illustrated in (A). By disposing the gas processing layer on only one surface of the conductive porous substrate, it is possible to prevent the conductive porous substrate from becoming wet with water, thereby enabling smooth gas supply from the conductive porous substrate to the gas processing layer.

It is desirable to use a conductive gas diffusion layer (GDL) for the conductive porous substrate. An example of a conductive gas diffusion layer is carbon paper.

The gas treatment layer contains at least one of a hydrogen storage alloy and a precious metal catalyst. The gas treatment layer is capable of treating hydrogen gas by being electrically connected to the positive electrode. The hydrogen storage alloy is not particularly limited as long as it can store hydrogen. Examples of hydrogen storage alloys include _LaNi5- based _alloys such as _LaNi4.7Al0.3 .

An example of the hydrogen storage reaction in a gas treatment layer containing a hydrogen storage alloy is shown in reaction formula (D) below.

Reaction formula (D) can occur when _E0 is a potential of −0.83 V. The reaction formula (E) below shows the reaction between the gas treatment layer containing a hydrogen storage alloy and the positive electrode containing LiMn ₂ O ₄ as the positive electrode active material.

The electromotive force E of reaction equation (E) is 1.78 V.

The noble metal catalyst is not particularly limited as long as it promotes the oxidation reaction of H _2. An example of the noble metal catalyst is a platinum catalyst supported on a carbon material (Pt/C).

A gas processing layer containing a precious metal catalyst can be obtained, for example, by dispersing the precious metal catalyst and a binder in a solvent to prepare a paste, applying the resulting paste to a conductive porous substrate, and drying it. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), perfluoroalkylsulfonic acid polymers, and fluorine-based ion exchange membranes. One or more types of binders can be used. Examples of solvents include organic solvents such as N-methylpyrrolidone (NMP).
(positive electrode)
The positive electrode includes a positive electrode current collector and a positive electrode mixture layer (positive electrode active material-containing layer) carried on at least one surface of the positive electrode current collector.

The positive electrode mixture layer can be formed on one or both sides of the current collector. The positive electrode mixture layer can contain a positive electrode active material and, optionally, a conductive material and a binder.

For example, oxides or sulfides can be used as the positive electrode active material. The positive electrode may contain one type of compound alone as the positive electrode active material, or may contain a combination of two or more types of compounds. Examples of oxides and sulfides include compounds that can insert and extract Li or Li ions.

Examples of such compounds include manganese dioxide (MnO ₂ ), iron oxide, copper oxide, nickel oxide, lithium manganese composite oxides (e.g., Li _x Mn ₂ O ₄ or Li _x MnO ₂ ; 0<x≦1), lithium nickel composite oxides (e.g., Li _x NiO ₂ ; 0<x≦1), lithium cobalt composite oxides (e.g., Li _x CoO ₂ ; 0<x≦1), lithium nickel cobalt composite oxides (e.g., Li _x Ni _1-y Co _y O ₂ ; 0<x≦1, 0<y<1), lithium manganese cobalt composite oxides (e.g., Li _x Mn _y Co _1-y O ₂ ; 0<x≦1, 0<y<1), and lithium manganese nickel composite oxides having a spinel structure (e.g., Li _x Mn _2-y Ni _y O ₄ ; 0<x≦1, 0<y< ₂ ), _lithium phosphate oxides having an olivine structure (e.g., _LixFePO4 ; 0<x≦1 _{, LixFe1-yMnyPO4} ; 0<x≦1, ₀ <y< ₁ , _LixCoPO4 ; 0<x≦1), iron sulfate ( _Fe2 ( _SO4 ) ₃ ), vanadium oxides (e.g., _V2O5 ), and lithium _{nickel cobalt manganese} composite oxides ( _{LixNi1- yzCoyMnzO2} ; 0<x≦1, 0<y< ₁ , ₀ <z<1, y+z<1).

Among the above, examples of more preferred compounds as the positive electrode active material include lithium manganese composite oxides having a spinel structure (e.g., Li _x Mn ₂ O ₄ ; 0<x≦1), lithium nickel composite oxides (e.g., Li _x NiO ₂ ; 0<x≦1), lithium cobalt composite oxides (e.g., Li _x CoO ₂ ; 0<x≦1), lithium nickel cobalt composite oxides (e.g., Li _x Ni _1-y Co _y O ₂ ; 0<x≦1, 0<y<1), lithium manganese nickel composite oxides having a spinel structure (e.g., Li _x Mn _2-y Ni _y O ₄ ; 0<x≦1, 0<y<2), lithium manganese cobalt composite oxides (e.g., Li _x Mn _y Co _1-y O ₂ ; 0<x≦1, 0<y<1), and lithium iron phosphate (e.g., Li _x FePO ₄ ; 0<x≦1) and lithium nickel cobalt manganese composite oxide (Li _x Ni _1-yz Co _y Mn _z O ₂ ; 0<x≦1, 0<y<1, 0<z<1, y+z<1). When these compounds are used as the positive electrode active material, the positive electrode potential can be increased.

When a room temperature molten salt is used as the battery electrolyte, it is preferable to use a positive electrode active material containing lithium iron phosphate, Li _x VPO ₄ F (0≦x≦1), lithium manganese composite oxide, lithium nickel composite oxide, lithium nickel cobalt composite oxide, or a mixture thereof.

The primary particle size of the positive electrode active material is preferably 100 nm or more and 1 μm or less. Positive electrode active materials with a primary particle size of 100 nm or more are easy to handle in industrial production. Positive electrode active materials with a primary particle size of 1 μm or less allow lithium ions to diffuse smoothly within the solid.

The specific surface area of the positive electrode active material is preferably 0.1 ^m /g or more and 10 ^m /g or less. A positive electrode active material having a specific surface area of 0.1 m/g or more can ensure sufficient sites for occlusion and desorption of Li ions. A positive electrode active material having a specific surface area of ^{10 m} /g or less is easy to handle in industrial production and can ensure good charge-discharge cycle performance.

The binder is added to fill the gaps between the dispersed positive electrode active material and to bind the positive electrode active material to the positive electrode current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-containing rubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and salts of CMC. One of these may be used as the binder, or two or more may be used in combination as binders.

The conductive material is blended to improve current collection performance and reduce contact resistance between the positive electrode active material and the positive electrode current collector. Examples of conductive materials include vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, graphite, carbonaceous materials such as carbon nanofibers and carbon nanotubes. One of these may be used as the conductive material, or two or more may be combined and used as the conductive material. The conductive material may also be omitted.

In the positive electrode mixture layer, the positive electrode active material and binder are preferably blended in proportions of 80% by mass or more and 98% by mass or less, and 2% by mass or more and 20% by mass or less, respectively.

By using a binder amount of 2% by mass or more, sufficient electrode strength can be achieved. The binder can also function as an insulator. Therefore, by using a binder amount of 20% by mass or less, the amount of insulator contained in the electrode is reduced, thereby reducing internal resistance.

When a conductive material is added, the positive electrode active material, binder, and conductive material are preferably blended in proportions of 77% by mass or more and 95% by mass or less, 2% by mass or more and 20% by mass or less, and 3% by mass or more and 15% by mass or less, respectively.

By setting the amount of conductive material to 3% by mass or more, the above-mentioned effects can be achieved. Furthermore, by setting the amount of conductive material to 15% by mass or less, the proportion of conductive material in contact with the electrolyte can be reduced. This low proportion can reduce decomposition of the electrolyte during high-temperature storage.
The positive electrode current collector is made of, for example, a material that is electrochemically stable at the potential at which lithium (Li) is inserted and extracted from the active material. For example, the positive electrode current collector can be nickel, stainless steel, aluminum, an aluminum alloy (e.g., an aluminum alloy containing one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si), or a metal foil containing one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si. The thickness of the positive electrode current collector is preferably 5 μm or more and 20 μm or less. A current collector having such a thickness can balance the strength and weight of the electrode.

The current collector may include a portion on the surface of which no composite layer is formed, and this portion may function as a current collecting tab or a current collecting lead.
(Negative electrode)
The negative electrode includes a negative electrode current collector and a negative electrode mixture layer (negative electrode active material-containing layer) carried on at least one surface of the negative electrode current collector.

The negative electrode mixture layer can be formed on one or both sides of the negative electrode current collector. The negative electrode mixture layer can contain a negative electrode active material and, optionally, a conductive material and a binder.

Examples of negative electrode active materials include lithium titanate having a ramsdellite structure (e.g., Li2 _{+ yTi3O7} , 0≦y≦3), lithium titanate having a spinel structure (e.g., _{Li4 + xTi5O12} , 0 _≦ x≦3), monoclinic titanium dioxide ( _TiO2 (B)), anatase titanium dioxide, rutile titanium dioxide, _niobium pentoxide ( _Nb2O5 ), hollandite titanium composite oxide, orthorhombic titanium-containing composite oxide, and monoclinic niobium titanium composite oxide.

An example of an orthorhombic titanium-containing composite oxide is a compound represented by Li2 ₊ aM(I) _{2- bTi6-cM} (II) _{dO14 +σ} . Here, M(I) is at least one selected from the group consisting of Sr, Ba, Ca, Mg, Na, Cs, Rb, and K. M(II) is at least one selected from the group consisting of Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni, and Al. The subscripts in the composition formula are 0≦a≦6, 0≦b<2, 0≦c<6, 0≦d<6, and -0.5 _{≦σ≦0.5. A specific example of an orthorhombic titanium-containing composite oxide is Li2+aNa2Ti6O14 ( 0 ≦} a≦6).

An example of the monoclinic niobium titanium composite oxide is a compound represented by Li _x Ti _1-y M1 _y Nb _2-z M2 _z O _7+δ . Here, M1 is at least one selected from the group consisting of Zr, Si, and Sn. M2 is at least one selected from the group consisting of V, Ta, and Bi. The subscripts in the composition formula are 0≦x≦5, 0≦y<1, 0≦z<2, and −0.3≦δ≦0.3. A specific example of the monoclinic niobium titanium composite oxide is Li _x Nb ₂ TiO ₇ (0≦x≦5).

Another example of a monoclinic niobium titanium composite oxide is a compound represented by Li _x Ti _1-y M3 _y+z Nb _2-z O _7-δ , where M3 is at least one selected from Mg, Fe, Ni, Co, W, Ta, and Mo. The subscripts in the composition formula are 0≦x≦5, 0≦y<1, 0≦z<2, and −0.3≦δ≦0.3.

Conductive materials are added to improve current collection performance and reduce contact resistance between the active material and the current collector. Examples of conductive materials include carbonaceous materials such as vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, graphite, carbon nanofibers, and carbon nanotubes. One of these may be used as the conductive material, or two or more may be combined. Alternatively, instead of using a conductive material, the surfaces of the active material particles may be coated with carbon or an electronically conductive inorganic material.

The binder is added to fill the gaps between the dispersed active material and to bind the active material and the negative electrode current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, styrene-butadiene rubber (SBR), polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and CMC salts. One of these may be used as the binder, or two or more may be used in combination.

The blending ratios of the negative electrode active material, conductive material, and binder in the negative electrode mixture layer can be appropriately changed depending on the application of the negative electrode. For example, the negative electrode active material, conductive material, and binder are preferably blended in ratios of 68% by mass or more and 96% by mass or less, 2% by mass or more and 30% by mass or less, and 2% by mass or more and 30% by mass or less, respectively. By setting the amount of conductive material to 2% by mass or more, the current collection performance of the negative electrode mixture layer can be improved. Furthermore, by setting the amount of binder to 2% by mass or more, sufficient binding between the negative electrode mixture layer and the current collector can be achieved, and excellent cycle performance can be expected. On the other hand, it is preferable to set the amount of conductive material and binder to 30% by mass or less each in order to achieve high capacity.
The negative electrode current collector is preferably made of, for example, a material that is electrochemically stable at the potential at which lithium (Li) is inserted into and extracted from the active material. For example, the negative electrode current collector is preferably made of copper, nickel, stainless steel, aluminum, an aluminum alloy (e.g., an aluminum alloy containing one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si), or Zn foil. The surface of the Zn foil may be coated with a carbon-containing layer. The thickness of the negative electrode current collector is preferably 5 μm or more and 20 μm or less. A current collector having such a thickness can balance the strength and weight of the electrode.

The current collector may include a portion on whose surface no composite layer is formed. This portion can function as a current collecting tab or current collecting lead.

(aqueous electrolyte)
The solvent for the aqueous electrolyte is a solvent containing water, and may consist of water alone or water and a solvent other than water. Examples of the solvent other than water include water-soluble organic solvents. Examples of water-soluble organic solvents include γ-butyrolactone, acetonitrile, alcohols, N-methylpyrrolidone (NMP), dimethylacetamide, dimethyl sulfoxide, and tetrahydrofuran. The type of solvent contained in the aqueous solvent for the electrolyte may be one or more types. In the aqueous solvent for the electrolyte, the content of the solvent other than water is preferably 20 wt % or less.

The presence of water in aqueous electrolytes can be confirmed by GC-MS (Gas Chromatography-Mass Spectrometry). Furthermore, the salt concentration and water content in aqueous electrolytes can be measured, for example, using ICP (Inductively Coupled Plasma) optical emission spectrometry. The molar concentration (mol/L) can be calculated by weighing a specified amount of aqueous electrolyte and calculating the salt concentration. Furthermore, the number of moles of solute and solvent can be calculated by measuring the specific gravity of the aqueous electrolyte.

The alkali metal salt contained in the aqueous electrolyte is, for example, one or more alkali metal salts selected from the group consisting of Li, Na, and K. Li, Na, and K each have excellent ionic conductivity, and therefore can increase the ionic conductivity of the aqueous electrolyte. The type of alkali metal salt in the aqueous electrolyte can be one or more types. It is more preferable that Li ⁺ is obtained as the alkali metal ion by dissolving the alkali metal salt in an aqueous solvent. For this reason, it is more preferable to use a lithium salt as the alkali metal salt in the aqueous electrolyte.
In the aqueous electrolyte, the concentration of alkali metal ions in the aqueous solvent is preferably 1 mol/L or more and 12 mol/L or less. By increasing the concentration of alkali metal ions, the number of free water molecules in the aqueous electrolyte is reduced, and hydrogen generation can be suppressed. Furthermore, even within the above-mentioned range, the concentration of alkali metal ions in the aqueous solvent is preferably 4 mol/L or more, and more preferably 5 mol/L or more. Furthermore, even within the above-mentioned range, the concentration of alkali metal ions in the aqueous solvent is preferably 10 mol/L or less.
The alkali metal salt of the aqueous electrolyte is, for example, a lithium salt. Examples of lithium salts include LiCl, LiBr, LiOH, _Li2SO4 , _LiNO3 , _{Li2C2O4 , Li2CO3} , Li[( _FSO2 ) _2N ], Li[( _CF3SO2 ) _2N ] _{, and} LiB[(OCO) ₂ ] ₂ . _{One or} more types of lithium salts may be used. The lithium salt used is preferably a lithium salt containing LiCl, LiOH, _Li [( _FSO2 ) _2N ], or Li[( _CF3SO2 ) _2N ].

The anion of _{the alkali metal salt in the aqueous electrolyte may include, for example, one or more ions selected from the group consisting of Cl-, Br-, OH-, SO42-} ^{, NO3- , C2O42- ,} _CO32- ^{, [} _{( FSO2 ) 2N ] -} ^, [( _CF3SO2 ) _2N ] ^-, and B[(OCO) ₂ ] ^2- . In particular, the anion preferably includes one or more ions selected from the group consisting of Cl- ^, _OH- ^, [( _FSO2 ) _2N ] ^-, and [( _CF3SO2 ) _2N ] ^- . This increases the concentration of alkali metal ions, thereby suppressing hydrogen generation at the negative electrode. This increases the charge/discharge efficiency (Coulombic efficiency) of the battery and significantly improves storage performance and cycle life.

The aqueous electrolyte may also be a gel electrolyte containing a complex of the aforementioned alkali metal salt and a polymer material. When the aqueous electrolyte is a gel electrolyte, the diffusion of water molecules from the aqueous electrolyte to the negative electrode can be suppressed, significantly suppressing hydrogen generation at the negative electrode. This significantly improves the cycle life and storage performance of the battery. The complex is, for example, a gel electrolyte formed by complexing an aqueous solution in which the aforementioned alkali metal salt is dissolved in an aqueous solvent with a polymer material. Examples of polymer materials that can be complexed with the alkali metal salt include polyacrylates (e.g., lithium polyacrylate, potassium polyacrylate, etc.), polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), and polyethylene oxide (PEO). One or more types of polymer material can be used. The polymer material can be in the form of, for example, granules or fibers. The content of the polymer material in the electrolyte can be in the range of 0.5% by weight to 10% by weight.

The secondary battery of the embodiment may further include a separator, an exterior member, a positive electrode terminal, or a negative electrode terminal. The separator, the exterior member, the positive electrode terminal, and the negative electrode terminal will be described below.
(separator)
The separator is disposed, for example, between the positive electrode and the negative electrode. Alternatively, a portion of the separator may be in contact with either the positive electrode or the negative electrode instead of being disposed between the positive electrode and the negative electrode.

The separator is formed, for example, from a porous film containing polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), cellulose, or polyvinylidene fluoride (PVdF), or a synthetic resin nonwoven fabric. Separators made of porous film coated with inorganic or organic compounds can also be used. From a safety perspective, it is preferable to use a porous film made of polyethylene or polypropylene. This is because these porous films melt at a certain temperature and are capable of interrupting electrical current.

The separator may be, for example, a plurality of separators each disposed between a positive electrode and a negative electrode, or may be a single separator folded zigzag, in which case the positive electrodes and negative electrodes are alternately disposed in the spaces formed by folding the separator.
(Exterior member)
The exterior member may be, for example, a container made of a laminate film or a metal container.

The thickness of the laminate film is, for example, 0.5 mm or less, and preferably 0.2 mm or less.

The laminate film used is a multilayer film containing multiple resin layers with metal layers sandwiched between them. The resin layers include polymeric materials such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET). The metal layers are preferably made of aluminum foil or aluminum alloy foil to reduce weight. The laminate film can be molded into the shape of the exterior component by sealing it with heat.

The wall thickness of the metal container is, for example, 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.2 mm or less.

The metal container is made of, for example, aluminum or an aluminum alloy. The aluminum alloy preferably contains elements such as magnesium, zinc, and silicon. If the aluminum alloy contains transition metals such as iron, copper, nickel, and chromium, the content is preferably 100 ppm by mass or less. Batteries equipped with such a metal container can dramatically improve long-term reliability and heat dissipation in high-temperature environments.

The shape of the exterior member is not particularly limited. The shape of the exterior member may be, for example, flat (thin), rectangular, cylindrical, coin-shaped, button-shaped, sheet-shaped, laminated, or the like. The exterior member can be appropriately selected depending on the battery dimensions and the application of the battery. For example, the exterior member may be an exterior member for a small battery mounted in a portable electronic device or the like. Alternatively, the exterior member may be an exterior member for a large battery mounted in a vehicle such as a two-wheeled or four-wheeled automobile.
(Negative terminal)
The negative electrode terminal can be formed from a material that is electrically stable and conductive in a potential range of 0.8 V to 3 V relative to the redox potential of lithium (vs. Li/Li ⁺ ). Specific examples of the material for the negative electrode terminal include copper, nickel, stainless steel, aluminum, and aluminum alloys containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. Aluminum or an aluminum alloy is preferably used as the material for the negative electrode terminal. The negative electrode terminal is preferably made of the same material as the negative electrode current collector in order to reduce contact resistance with the negative electrode current collector.
(positive terminal)
The positive electrode terminal can be formed from a material that is electrically stable and conductive in a potential range of 3 V to 4.5 V relative to the redox potential of lithium (vs. Li/Li ⁺ ). Examples of materials for the positive electrode terminal include titanium, aluminum, and aluminum alloys containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. The positive electrode terminal is preferably formed from the same material as the positive electrode current collector in order to reduce contact resistance with the positive electrode current collector.

The secondary battery of the first embodiment described above includes a gas processing structure that can process hydrogen gas by conducting with the positive electrode, thereby suppressing an increase in internal pressure and improving charge/discharge efficiency.

Second Embodiment
According to a second embodiment, a battery pack including the battery according to the embodiment is provided. This battery pack may include a battery assembly including the battery according to the embodiment. This battery pack may include a single battery instead of the battery assembly.

Such a battery pack may further include a protection circuit. The protection circuit has the function of controlling the charging and discharging of the secondary battery. Alternatively, a circuit included in a device that uses the battery pack as a power source (e.g., electronic equipment, automobiles, etc.) may be used as the protection circuit for the battery pack.

The battery pack may also be equipped with external terminals for current flow. The external terminals for current flow are for outputting current from the secondary battery to the outside and/or inputting current from the outside to the secondary battery. In other words, when the battery pack is used as a power source, current is supplied to the outside through the external terminals for current flow. Furthermore, when the battery pack is charged, charging current (including regenerative energy from the power of an automobile, etc.) is supplied to the battery pack through the external terminals for current flow.

Next, an example of a battery pack according to an embodiment will be described with reference to the drawings.

The battery pack 300 shown in Figures 9 and 10 includes a container 31, a lid 32, a protective sheet 33, a battery pack 200, a printed wiring board 34, wiring 35, and an insulating plate (not shown).

The storage container 31 shown in FIG. 9 is a bottomed, square container with a rectangular bottom. The storage container 31 is configured to be able to accommodate a protective sheet 33, a battery pack 200, a printed wiring board 34, and wiring 35. The lid 32 has a rectangular shape. The lid 32 covers the storage container 31 to accommodate the battery pack 200 and other components. Although not shown, the storage container 31 and the lid 32 are provided with openings or connection terminals for connecting to external devices, etc.

The battery pack 200 includes multiple cells 100, a positive electrode lead 207, a negative electrode lead 206, and adhesive tape 36.

At least one of the multiple cells 100 is a secondary battery according to the embodiment. Each of the multiple cells 100 is electrically connected in series as shown in FIG. 10 . The multiple cells 100 may be electrically connected in parallel, or may be connected in a combination of series and parallel connections. Connecting multiple cells 100 in parallel increases battery capacity compared to connecting them in series.

Adhesive tape 36 fastens the multiple cells 100 together. Instead of adhesive tape 36, heat-shrinkable tape may be used to secure the multiple cells 100 together. In this case, protective sheets 33 are placed on both sides of the battery pack 200, heat-shrinkable tape is wrapped around the cells, and the heat-shrinkable tape is then thermally shrunk to bind the multiple cells 100 together.

One end of the positive electrode lead 207 is connected to the battery pack 200. One end of the positive electrode lead 207 is electrically connected to the positive electrode of one or more cells 100. One end of the negative electrode lead 206 is connected to the battery pack 200. One end of the negative electrode lead 206 is electrically connected to the negative electrode of one or more cells 100.

The printed wiring board 34 is installed along one of the shorter sides of the inner surface of the container 31. The printed wiring board 34 includes a positive connector 342, a negative connector 343, a thermistor 345, a protection circuit 346, wiring 342a and 343a, an external terminal 350 for supplying current, a positive wiring (positive wiring) 348a, and a negative wiring (negative wiring) 348b. One main surface of the printed wiring board 34 faces one side of the battery pack 200. An insulating plate (not shown) is interposed between the printed wiring board 34 and the battery pack 200.

The other end 207a of the positive electrode lead 207 is electrically connected to the positive electrode connector 342. The other end 206a of the negative electrode lead 206 is electrically connected to the negative electrode connector 343.

The thermistor 345 is fixed to one main surface of the printed wiring board 34. The thermistor 345 detects the temperature of each battery cell 100 and transmits the detection signal to the protection circuit 346.

The external terminals 350 for current flow are fixed to the other main surface of the printed wiring board 34. The external terminals 350 for current flow are electrically connected to devices external to the battery pack 300. The external terminals 350 for current flow include a positive terminal 352 and a negative terminal 353.

The protection circuit 346 is fixed to the other main surface of the printed wiring board 34. The protection circuit 346 is connected to the positive terminal 352 via the positive wiring 348a. The protection circuit 346 is connected to the negative terminal 353 via the negative wiring 348b. The protection circuit 346 is also electrically connected to the positive connector 342 via wiring 342a. The protection circuit 346 is electrically connected to the negative connector 343 via wiring 343a. The protection circuit 346 is also electrically connected to each of the multiple cells 100 via wiring 35.

The protective sheet 33 is arranged on both inner surfaces of the long sides of the container 31 and on the inner surface of the short side that faces the printed wiring board 34 via the battery pack 200. The protective sheet 33 is made of, for example, resin or rubber.

The protection circuit 346 controls the charging and discharging of the multiple cells 100. Furthermore, the protection circuit 346 cuts off the electrical connection between the protection circuit 346 and the external terminals 350 (positive terminal 352, negative terminal 353) for supplying electricity to external devices based on a detection signal transmitted from the thermistor 345 or a detection signal transmitted from an individual cell 100 or the battery pack 200.

Examples of detection signals transmitted from the thermistor 345 include signals detecting that the temperature of a cell 100 is equal to or higher than a predetermined temperature. Examples of detection signals transmitted from an individual cell 100 or the battery pack 200 include signals detecting overcharge, overdischarge, and overcurrent of a cell 100. When detecting overcharge, etc. for an individual cell 100, the battery voltage may be detected, or the positive electrode potential or negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each cell 100.

The protection circuit 346 may also be a circuit included in a device (e.g., electronic equipment, automobile, etc.) that uses the battery pack 300 as a power source.

Furthermore, as described above, the battery pack 300 is equipped with the external terminal 350 for current flow. Therefore, the battery pack 300 can output current from the battery assembly 200 to an external device and input current from the external device to the battery assembly 200 via the external terminal 350 for current flow. In other words, when the battery pack 300 is used as a power source, current from the battery assembly 200 is supplied to the external device via the external terminal 350 for current flow. Furthermore, when charging the battery pack 300, charging current from the external device is supplied to the battery pack 300 via the external terminal 350 for current flow. When the battery pack 300 is used as an in-vehicle battery, regenerative energy from the vehicle's power can be used as charging current from the external device.

The battery pack 300 may include multiple battery assemblies 200. In this case, the multiple battery assemblies 200 may be connected in series, in parallel, or in a combination of series and parallel connections. The printed wiring board 34 and wiring 35 may also be omitted. In this case, the positive electrode lead 207 and the negative electrode lead 206 may be used as the positive and negative terminals of the external terminals for current flow, respectively.

Such battery packs are used in applications that require excellent cycle performance, for example, when drawing large currents. Specific examples of such battery packs include power sources for electronic devices, stationary batteries, and on-board batteries for various vehicles. Examples of electronic devices include digital cameras. This battery pack is particularly suitable for use as an on-board battery.

The battery pack according to the second embodiment includes the secondary battery according to the embodiment. As a result, the battery pack can suppress an increase in internal pressure and improve charge/discharge efficiency.

[Third embodiment]
According to a third embodiment, a vehicle including a battery pack according to an embodiment is provided.

In such a vehicle, the battery pack, for example, recovers regenerative energy from the vehicle's motive power. The vehicle may also include a mechanism (regenerator) that converts the vehicle's kinetic energy into regenerative energy.

Examples of vehicles according to the present embodiment include two- to four-wheel hybrid electric vehicles, two- to four-wheel electric vehicles, power-assisted bicycles, and railcars.

The mounting location of the battery pack in the vehicle according to the embodiment is not particularly limited. For example, when the battery pack is mounted in an automobile, the battery pack can be mounted in the engine compartment, the rear of the vehicle body, or under the seat.

Vehicles according to embodiments may be equipped with multiple battery packs. In this case, the batteries included in each battery pack may be electrically connected in series, electrically connected in parallel, or electrically connected using a combination of series and parallel connections. For example, if each battery pack includes a battery assembly, the battery assembly may be electrically connected in series, electrically connected in parallel, or electrically connected using a combination of series and parallel connections. Alternatively, if each battery pack includes a single battery, the batteries may be electrically connected in series, electrically connected in parallel, or electrically connected using a combination of series and parallel connections.

Next, an example of a vehicle according to an embodiment will be described with reference to the drawings.

The vehicle 400 shown in FIG. 11 includes a vehicle body 40 and a battery pack 300 according to an embodiment. In the example shown in FIG. 11, the vehicle 400 is a four-wheeled automobile.

The vehicle 400 may be equipped with multiple battery packs 300. In this case, the batteries (e.g., single cells or battery packs) included in the battery packs 300 may be connected in series, in parallel, or in a combination of series and parallel connections.

Figure 11 illustrates an example in which the battery pack 300 is mounted in an engine compartment located in the front of the vehicle body 40. As mentioned above, the battery pack 300 may also be mounted, for example, at the rear of the vehicle body 400 or under a seat. This battery pack 300 can be used as a power source for the vehicle 400. In addition, this battery pack 300 can recover regenerative energy for powering the vehicle 400.

The vehicle according to the third embodiment is equipped with a battery pack according to the embodiment. Therefore, the vehicle can exhibit high performance and is highly reliable.

[Fourth embodiment]
According to a fourth embodiment, a stationary power source including a battery pack according to an embodiment is provided.

Such a stationary power source may be equipped with a battery pack according to an embodiment or a battery according to an embodiment instead of the battery pack according to an embodiment. Such a stationary power source can exhibit a long life.

Figure 12 is a diagram showing an example of application of battery packs 300A, 300B according to an embodiment to stationary power sources 112, 123. The example shown in Figure 12 illustrates a system 110 in which stationary power sources 112, 123 are used. System 110 includes a power plant 111, a stationary power source 112, a customer-side power grid 113, and an energy management system (EMS) 115. System 110 also includes a power grid 116 and a communication network 117, and power plant 111, stationary power source 112, customer-side power grid 113, and EMS 115 are connected via power grid 116 and communication network 117. EMS 115 utilizes power grid 116 and communication network 117 to perform control to stabilize the entire system 110.

The power plant 111 generates large amounts of electricity using fuel sources such as thermal and nuclear power. Power is supplied from the power plant 111 via the power grid 116, etc. The stationary power source 112 is equipped with a battery pack 300A. The battery pack 300A can store the power supplied from the power plant 111. The stationary power source 112 can supply the power stored in the battery pack 300A via the power grid 116, etc. The system 110 is also equipped with a power conversion device 118. The power conversion device 118 includes a converter, inverter, transformer, etc. Therefore, the power conversion device 118 can convert between direct current and alternating current, convert between alternating currents with different frequencies, and perform voltage transformation (boost and step-down). Therefore, the power conversion device 118 can convert power from the power plant 111 into power that can be stored in the battery pack 300A.

The consumer-side power system 113 includes a power system for factories, a power system for buildings, and a power system for homes. The consumer-side power system 113 includes a consumer-side EMS 121, a power conversion device 122, and a stationary power source 123. The stationary power source 123 is equipped with a battery pack 300B. The consumer-side EMS 121 performs control to stabilize the consumer-side power system 113.

The consumer-side power system 113 receives power from the power plant 111 and power from the battery pack 300A via the power grid 116. The battery pack 300B can store the power supplied to the consumer-side power system 113. Similarly to the power conversion device 118, the power conversion device 122 includes a converter, inverter, transformer, and the like. Therefore, the power conversion device 122 can convert between direct current and alternating current, convert between alternating currents with different frequencies, and perform voltage transformation (boost and step-down). Therefore, the power conversion device 122 can convert the power supplied to the consumer-side power system 113 into power that can be stored in the battery pack 300B.

The electricity stored in the battery pack 300B can be used, for example, to charge vehicles such as electric cars. The system 110 may also be equipped with a natural energy source. In this case, the natural energy source generates electricity using natural energy such as wind power and sunlight. Electricity is then supplied from the natural energy source in addition to the power plant 111 via the power grid 116.

[Example]
The above-described embodiment will be specifically explained below using examples, but the present invention is not limited to the following examples as long as they do not deviate from the gist of the present invention.
Example 1
(Preparation of Positive Electrode)
100 parts by weight of LiMn ₂ O ₄ powder was prepared as the positive electrode active material. 10 parts by weight of acetylene black was used as the conductive agent. 10 parts by weight of polyvinylidene fluoride (PVdF) was used as the binder. The positive electrode active material, conductive agent, and binder were then added to N-methylpyrrolidone (NMP) and mixed to prepare a slurry. The prepared slurry was then applied to both sides of a positive electrode current collector. A 15 μm thick titanium foil was used as the positive electrode current collector. After drying the slurry coating, the positive electrode current collector and coating were pressed together to prepare a positive electrode sheet. The prepared positive electrode sheet was punched out to obtain a positive electrode consisting of a 10 mm x 30 mm tab portion and a 30 mm x 40 mm electrode portion (portion where the positive electrode composite layer was formed).
(Preparation of negative electrode)
100 parts by weight of _{Li4Ti5O12 powder} was used as _the negative electrode active material, and 10 parts by weight of acetylene black was used as the conductive agent. 10 parts by weight of PVdF was used as the binder. The negative electrode active material, conductive agent, and binder were then added to NMP and mixed to prepare a slurry. The prepared slurry was then applied to both sides of the negative electrode current collector. The negative electrode current collector was made of zinc foil having a 1 μm thick carbon-containing coating layer, with a thickness of 15 μm. After drying the coating of the slurry, the negative electrode current collector and the coating were pressed to prepare a negative electrode sheet. The negative electrode sheet was punched out to form a negative electrode having a shape consisting of a 10 mm x 30 mm tab portion and a 30 mm x 40 mm electrode portion (negative electrode composite layer forming portion).
(Fabrication of secondary battery)
The positive and negative electrodes prepared as described above were alternately stacked to produce a stack as an electrode group. In the stack, a separator was interposed between the positive and negative electrodes. Hard filter paper was used as the separator. Terminals were ultrasonically welded to the tabs of each of the positive and negative electrodes. Titanium ribbon terminals were used for the positive electrode, and aluminum terminals with anodized surfaces were used for the negative electrode. The stack (electrode group) was then housed in an exterior member made of a laminate film. The laminate film used was a film in which polypropylene layers were formed on both sides of a 40 μm-thick aluminum foil.

A paste containing platinum-supported carbon and PvDF as a binder was applied to a 30 mm × 40 mm carbon paper sheet at a coating amount of 2.0 mg/ ^m2 and dried to form a gas-treating layer, thereby producing a gas-treating structure. A Ti wire was fixed to the carbon paper sheet with tape.

The gas processing structure was placed above the electrode group (stack body) at a certain distance from the electrode group. The Ti wire of the gas processing structure was fixed to the positive electrode terminal of the electrode group by ultrasonic welding, establishing electrical continuity between the gas processing structure and the positive electrode.

Then, 3 ml of a 12 M LiCl and 1 M LiOH aqueous solution was dropped onto the electrode assembly as an aqueous electrolyte. The laminate film exterior member was then completely sealed by heat sealing. This completed the production of a laminate cell-type aqueous lithium-ion secondary battery.
Example 2
7 , a PTFE sheet 25 having 3 mm wide and 0.3 mm deep grooves 24 arranged at equal intervals was placed on the side of the carbon paper 13 of the gas processing structure 5 where the gas processing layer was not provided. The grooves 24 of the PTFE sheet 25 were faced outward, and the side without the grooves was brought into contact with the carbon paper 13. Apart from this, a water-based lithium-ion secondary battery was fabricated in the same manner as in Example 1.
Example 3
A water-based lithium-ion secondary battery was fabricated in the same manner as in Example 2, except that a 10 Ω resistor was inserted between the Ti wire electrically connecting the carbon paper of the gas processing structure and the positive electrode terminal.
Example 4
An electrode assembly was fabricated in the same manner as in Example 1, except that the outermost layer of the electrode assembly was fabricated to be the positive electrode. A gas-processing structure was also fabricated in the same manner as described in Example 1. The gas-processing structure was laminated on the positive electrode positioned in the outermost layer of the electrode assembly so that the carbon paper was in contact with the positive electrode. The positive electrode and the gas-processing structure were not electrically connected with a Ti wire. Therefore, electrical conduction was achieved by directly contacting the gas-processing structure with the positive electrode. A water-based lithium-ion secondary battery was fabricated in the same manner as in Example 1, except for this.
Example 5
A positive electrode was fabricated in the same manner as in Example 1, except that _{LiNi0.5Co0.2Mn0.3O2} ( _NCM ) was used as the positive electrode active material. A water-based lithium _{- ion} secondary battery was fabricated in the same manner as in Example 1, except that the obtained positive electrode was used.
Example 6
Ten gas-processing structures fabricated in the same manner as in Example 2 were stacked. Ti wires were fixed to the carbon paper of each layer with tape, and the tips of the Ti wires were ultrasonically welded to the positive electrode terminal. A water-based lithium-ion secondary battery was fabricated in the same manner as in Example 1, except for this.
(Comparative Example 1)
A water-based lithium-ion secondary battery was fabricated in the same manner as in Example 1, except that the gas-processing structure was not provided.
(Comparative Example 2)
A water based lithium ion secondary battery was fabricated in the same manner as in Example 5, except that the gas processing structure was not provided.
(Battery evaluation)
The fabricated aqueous lithium-ion secondary battery was subjected to constant current charging at a current value of 1 C (100 mA in this example) in an environment of 25°C, with a charge potential of 2.7 V and a discharge potential of 2.1 V. The charging cycle was terminated after 1.1 hours (1.1 hours) had elapsed since the start of charging, or when the current value converged to 0.5 C (50 mA in this example) or less. The battery was discharged at a constant current of 1 C until the voltage reached 2.1 V. The above charge/discharge cycle was repeated 20 times, and the cell volume was measured before and after each cycle to calculate the amount of gas generated.

The charge-discharge efficiency (%) for each of the 20 charge-discharge cycles performed under the above conditions was calculated by 100 × {discharge capacity (mAh/g)/charge capacity ₍ mAh/ _g )}. The average of the calculated charge-discharge efficiencies is shown in Table 1. In Table 1, LMO represents _{LiMn2O4 , NCM} represents _{LiNi0.5Co0.2Mn0.3O2 ,} and TLO represents _{Li4Ti5O12 .}

As is clear from Table 1, the secondary batteries of Examples 1-6 equipped with a gas treatment structure had a smaller amount of gas after 20 charge/discharge cycles and a higher average charge/discharge efficiency than the secondary batteries of Comparative Examples 1 and 2, which did not have a gas treatment structure.

The secondary battery of at least one of these embodiments or examples is equipped with a gas processing structure that can process hydrogen gas by conducting with the positive electrode, thereby suppressing an increase in internal pressure and improving charge/discharge efficiency.

While several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments may be embodied in a variety of other forms, and various omissions, substitutions, and modifications may be made without departing from the spirit of the invention. These embodiments and their variations are within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims.

The following is a description of the invention according to the embodiment.

[1] a positive electrode;
a negative electrode;
an aqueous electrolyte;
a gas treatment structure capable of treating hydrogen gas by being electrically connected to the positive electrode.

[2] The secondary battery described in [1], wherein the gas processing structure includes a conductive porous substrate and a gas processing layer laminated on the porous substrate and containing at least one of a hydrogen storage alloy or a precious metal catalyst.

[3] The secondary battery described in [1], wherein the gas processing structure includes a conductive porous substrate, a gas processing layer laminated on one surface of the porous substrate and containing at least one of a hydrogen storage alloy or a precious metal catalyst, and a layer laminated on the other surface of the porous substrate and having a gas flow path.

[4] The secondary battery described in any one of [1] to [3], wherein the gas processing structure is electrically connected to the positive electrode via a resistor.

[5] The secondary battery described in any one of [1] to [3], wherein the gas processing structure is electrically connected to the positive electrode via a switching element.

[6] The secondary battery described in [2], wherein the porous substrate of the gas processing structure is in contact with the positive electrode.

[7] The secondary battery described in any one of [1] to [6] above, which is a lithium ion secondary battery.

[8] A battery pack comprising the secondary battery described in any one of [1] to [7].

[9] The battery pack described in [8], further including an external terminal for applying current and a protection circuit.

[10] The battery pack described in [8] or [9] includes a plurality of the secondary batteries, which are electrically connected in series, parallel, or a combination of series and parallel.

[11] A vehicle equipped with a battery pack described in any one of [8] to [10].

[12] The vehicle described in [11], including a mechanism for converting the kinetic energy of the vehicle into regenerative energy.

[13] A stationary power source equipped with the battery pack described in any one of [8] to [10].

DESCRIPTION OF SYMBOLS 1...Secondary battery, 2...Exterior member, 3...Laminate, 4...Electrode group, 5...Gas treatment structure, 6...Positive electrode terminal, 7...Negative electrode terminal, 8...Wiring, 8a...Wiring, 8b...Wiring, 8c...Wiring, 9...Resistor, 10...Positive electrode, 10a...Positive electrode current collector, 10b...Positive electrode mixture layer, 11...Negative electrode, 11a...Negative electrode current collector, 11b...Negative electrode mixture layer, 11c...Negative electrode tab, 12...Separator, 13...Porous substrate, 14...Gas treatment layer, 21...Switching element, 22...Conductive member, 22a...First conductive plate, 22b...Second conductive plate, 23...Electrolyte layer, 24...Gas Gas flow path, 25...layer, 26...one-way, 31...container, 32...lid, 33...protective sheet, 34...printed wiring board, 35...wiring, 36...adhesive tape, 40...vehicle body, 100...secondary battery, 110...system, 111...power plant, 112...stationary power source, 113...consumer-side power system, 115...energy management system (EMS), 115...energy management system, 116...power grid, 117...communication network, 118...power conversion device, 121...consumer-side EMS, 122...power conversion device, 123...stationary power source.

Claims (13)

A positive electrode and
a negative electrode;
an aqueous electrolyte;
a gas treatment structure capable of treating hydrogen gas by being electrically connected to the positive electrode. The secondary battery described in claim 1, wherein the gas processing structure includes a conductive porous substrate and a gas processing layer laminated on the porous substrate and containing at least one of a hydrogen storage alloy or a precious metal catalyst. The secondary battery described in claim 1, wherein the gas processing structure includes a conductive porous substrate, a gas processing layer laminated on one surface of the porous substrate and containing at least one of a hydrogen storage alloy or a precious metal catalyst, and a layer laminated on the other surface of the porous substrate and having a gas flow path. The secondary battery described in claim 1, wherein the gas processing structure is electrically connected to the positive electrode via a resistor. The secondary battery described in claim 1, wherein the gas processing structure is electrically connected to the positive electrode via a switching element. The secondary battery described in claim 2, wherein the porous substrate of the gas processing structure is in contact with the positive electrode. The secondary battery of claim 1 is a lithium ion secondary battery. A battery pack comprising the secondary battery described in any one of claims 1 to 7. The battery pack described in claim 8, further including an external terminal for applying current and a protection circuit. The battery pack of claim 9 comprises a plurality of the secondary batteries, the secondary batteries being electrically connected in series, in parallel, or in a combination of series and parallel. A vehicle equipped with the battery pack described in claim 8. The vehicle described in claim 11, including a mechanism for converting the kinetic energy of the vehicle into regenerative energy. A stationary power source comprising the battery pack according to claim 8.